PHNOM PENH, Cambodia ? A long-delayed Khmer Rouge genocide tribunal wrapped up its opening session Wednesday with judges saying they must agree on a list of witnesses before announcing when a full trial of the former head of the regime's notorious torture center will begin.

Kaing Guek Eav ? better known as Duch ? is charged with crimes against humanity. He is the first of five defendants from the ultracommunist regime that ruled Cambodia in the 1970s and turned it into a vast slave labor camp in which an estimated 1.7 million people died.

Three decades after the Khmer Rouge fell, the U.N.-assisted tribunal began a procedural session Tuesday to lay the groundwork for a full trial expected in March. The precise date has not been set, and details still need to be ironed out.

Duch, 66, oversaw the S-21 prison in Phnom Penh ? previously a school, now the Tuol Sleng Genocide Museum ? where 16,000 men, women and children were detained and tortured. Only a handful survived.

Judges had not decided whether to allow as evidence a short film shot by conquering Vietnamese forces as they entered Tuol Sleng prison in January 1979. The film, which shows decapitated bodies and previously unknown child survivors, was released by Vietnam in December.

One 69-year-old observer at the trial said the Khmer Rouge executed five members of his family, including his parents, on a single day in 1976 for refusing to hand over a cow to the authorities.

"I'm coming to see the court find justice through the law," said Na Uth, who traveled with 24 others from the northwestern province of Banteay Meanchey to watch the proceedings. "My anger never stops. I always think about it. I can't think straight."